The present invention relates to a method for the control of an electrolytic display cell by means of electrical magnitude controlled by a reference electrode and to an apparatus for performing this method. It can be used in the display of alphanumeric characters or the like.
An electrolytic display cell comprising an electrolyte (generally a metal salt) inserted between the appropriately shaped semi-transparent electrodes and a counter electrode. A power supply makes it possible to raise the electrodes to a given potential in order to bring about either the deposition of a metal film (for the display of a character) or the redissolving of this film (for the erasure of the displayed character).
The electrical magnitudes applied (currents or voltages) either during writing and erasure, or optionally during the periods when the written or erased states are maintained must be accurately controlled because the display quality is dependent thereon. Thus, in such display means, the thickness of the deposited metal film is directly proportional to the electrical charge which has passed through the cell and the erasure of this film makes it necessary for an identical charge to traverse the cell in opposite directions. An inadequate charge on erasure leads to an accumulation of metal on the electrode and conversely an excessive charge or erasure can lead to secondary reactions in the electrolyte.
However, the currents and voltages applied to an electrolyte display cell are liable to vary when the operating conditions change (particularly with temperature) or when the cell itself changes (in the composition of its electrolyte for example) or on passing from one cell to another cell due to dispersions which can affect certain components (particularly the surface state of the electrodes) or finally when the electrolyte is changed although the cell is the same. Thus, in practice, it is difficult to maintain the control magnitudes at their most appropriate value.